Coated articles and methods

ABSTRACT

Coated articles and methods for applying coatings are described. In some cases, the coating can exhibit desirable properties and characteristics such as durability, corrosion resistance, and high conductivity. The articles may be coated, for example, using an electrodeposition process.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/500,786 (now U.S. Pat. No. 8,652,649), filed Jul. 10, 2009, which isincorporated herein by reference in its entirety.

FIELD OF INVENTION

The present invention generally relates to coated articles and relatedmethods. In some embodiments, the articles are coated using anelectrodeposition process.

BACKGROUND OF INVENTION

Many types of coatings may be applied on a base material.Electrodeposition is a common technique for depositing such coatings.Electrodeposition generally involves applying a voltage to a basematerial placed in an electrodeposition bath to reduce metal ionicspecies within the bath which deposit on the base material in the formof a metal, or metal alloy, coating. The voltage may be applied betweenan anode and a cathode using a power supply. At least one of the anodeor cathode may serve as the base material to be coated. In someelectrodeposition processes, the voltage may be applied as a complexwaveform such as in pulse plating, alternating current plating, orreverse-pulse plating.

A variety of metal and metal alloy coatings may be deposited usingelectrodeposition. For example, metal alloy coatings can be based on twoor more transition metals including Ni, W, Fe, Co, amongst others.

Corrosion processes, in general, can affect the structure andcomposition of an electroplated coating that is exposed to the corrosiveenvironment. For example, corrosion can involve direct dissolution ofatoms from the surface of the coating, a change in surface chemistry ofthe coating through selective dissolution or de-alloying, or a change insurface chemistry and structure of the coating through, e.g., oxidationor the formation of a passive film. Some of these processes may changethe topography, texture, properties or appearance of the coating. Forexample, spotting and/or tarnishing of the coating may occur. Sucheffects may be undesirable, especially when the coating is applied atleast in part to improve electrical conductivity since these effects canincrease the resistance of the coating.

SUMMARY OF INVENTION

Coated articles and related methods are provided.

In one aspect, a method is provided. The method compriseselectrodepositing a first layer of a coating on a base material using awaveform having a forward pulse and a reverse pulse, wherein the basematerial comprises copper, the first layer comprises Ni and the firstlayer comprises W and/or Mo, and the first layer has a thickness ofgreater than 5 microinches. The method further compriseselectrodepositing a second layer of the coating on the first layer, thesecond layer comprising a metal selected from the group consisting ofAu, Ru, Os, Rh, Ir, Pd, Pt, and/or Ag, the second layer having athickness of less than 30 microinches.

In another aspect, an article is provided. The article comprises a basematerial comprising copper. The article further comprises a coatingformed on the base material, the coating comprising a first layercomprising Ni, and W and/or Mo, wherein the first layer has a thicknessof greater than 5 microinches, and a second layer formed on the firstlayer, the second layer comprising a metal selected from the groupconsisting of Au, Ru, Os, Rh, Ir, Pd, Pt, and/or Ag, wherein the secondlayer has a thickness of less than 30 microinches.

Other aspects, embodiments and features of the invention will becomeapparent from the following detailed description when considered inconjunction with the accompanying drawings. The accompanying figures areschematic and are not intended to be drawn to scale. For purposes ofclarity, not every component is labeled in every figure, nor is everycomponent of each embodiment of the invention shown where illustrationis not necessary to allow those of ordinary skill in the art tounderstand the invention. All patent applications and patentsincorporated herein by reference are incorporated by reference in theirentirety. In case of conflict, the present specification, includingdefinitions, will control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a coated article according to some embodiments;

FIGS. 2A-2C show photographs of coated articles as described in Example1;

FIGS. 3A-3C show a test procedure and photographs of coated articles asdescribed in Example 2;

FIGS. 4A-4D show photographs of coated articles as described in Example3;

FIGS. 5A-5D show plots of contact resistance measurements as describedin Example 4;

FIGS. 6-7 shows photographs of coated articles as described in Example5;

FIGS. 8A-9B show plots of contact resistance measurements as describedin Example 5.

DETAILED DESCRIPTION

Coated articles and methods for applying coatings are described. Thearticle may include a base material and a multi-layer coating formedthereon. In some cases, the coating includes a first layer thatcomprises am alloy (e.g., nickel-tungsten alloy) and a second layer thatcomprises a precious metal (e.g., Ru, Os, Rh, Ir, Pd, Pt, Ag, and/orAu). In some cases, the coating may be applied using anelectrodeposition process. The coating can exhibit desirable propertiesand characteristics such as durability, corrosion resistance, and highconductivity, which may be beneficial, for example, in electricalapplications. In some cases, the presence of the first layer may allowfor a reduction in the thickness of the second layer while preservingthe desirable properties.

FIG. 1 shows an article 10 according to an embodiment. The article has acoating 20 formed on a base material 30. The coating may comprise afirst layer 40 formed on the base material and a second layer 50 formedon the first layer. Each layer may be applied using a suitable process,as described in more detail below. It should be understood that thecoating may include more than two layers. However, in some embodiments,the coating may only include two layers, as shown.

In some embodiments, the first layer comprises one or more metals. Forexample, the first layer may comprise a metal alloy. In some cases,alloys that comprise nickel are preferred. Such alloys may also comprisetungsten and/or molybdenum. Nickel-tungsten alloys may be preferred insome cases.

In some cases, the weight percent of nickel in the alloy may be between25-75 weight percent; and, in some cases, between 50 and 70 weightpercent. In these cases, the remainder of the alloy may be tungstenand/or molybdenum. Other weight percentages outside of this range may beused as well.

The first layer may have any thickness suitable for a particularapplication. For example, the first layer thickness may be greater thanabout 1 microinch (e.g., between about 1 microinch and about 100microinches, between about 1 microinch and 50 microinches); in somecases, greater than about 5 microinches (e.g., between about 5microinches and about 100 microinches, between about 5 microinches and50 microinches); greater than about 25 microinches (e.g., between about25 microinches and about 100 microinches, between about 1 microinch and50 microinches). It should be understood that other first layerthicknesses may also be suitable. In some embodiments, the thickness ofthe first layer is chosen such that the first layer is essentiallytransparent on the surface. Thickness may be measured by techniquesknown to those in the art.

In some embodiments, it may preferable for the first layer to be formeddirectly on the base material. Such embodiments may be preferred overcertain prior art constructions that utilize a layer between the firstlayer and the base material because the absence of such an interveninglayer can save on overall material costs. Though, it should beunderstood that in other embodiments, one or more layers may be formedbetween the first layer and the base material.

The second layer may comprise one or more precious metals. Examples ofsuitable precious metals include Ru, Os, Rh, Ir, Pd, Pt, Ag, and/or Au.Gold may be preferred in some embodiments. In some embodiments, thesecond layer consists essentially of one precious metal. In someembodiments, it may be preferable that the second layer is free of tin.In other cases, the second layer may comprise an alloy that includes atleast one precious metal and at least one other metal. The metal may beselected from Ni, W, Fe, B, S, Co, Mo, Cu, Cr, Zn and Sn, amongstothers.

The second layer may have any suitable thickness. It may be advantageousfor the second layer to be thin, for example, to save on material costs.For example, the second layer thickness may be less than 30 microinches(e.g., between about 1 microinch and about 30 microinches; in somecases, between about 5 microinches and about 30 microinches); in somecases the second layer thickness may be less than 20 microinches (e.g.,between about 1 microinch and about 20 microinches; in some cases,between about 5 microinches and about 20 microinches); and, in somecases, the second layer thickness may be less than 10 microinches (e.g.,between about 1 microinch and about 10 microinches; in some cases,between about 5 microinches and about 10 microinches). In someembodiments, the thickness of the second layer is chosen such that thesecond layer is essentially transparent on the surface. It should beunderstood that other second layer thicknesses may also be suitable.

The second layer may cover the entire first layer. However, it should beunderstood that in other embodiments, the second layer covers only partof the first layer. In some cases, the second layer covers at least 50%of the surface area of the first layer; in other cases, at least 75% ofthe surface area of the first layer. In some cases, an element from thefirst layer may be incorporated within the second layer and/or anelement from the second layer may be incorporated into the first layer.

In some cases, the coating (e.g., the first layer and/or the secondlayer) may have a particular microstructure. For example, at least aportion of the coating may have a nanocrystalline microstructure. Asused herein, a “nanocrystalline” structure refers to a structure inwhich the number-average size of crystalline grains is less than onemicron. The number-average size of the crystalline grains provides equalstatistical weight to each grain and is calculated as the sum of allspherical equivalent grain diameters divided by the total number ofgrains in a representative volume of the body. In some embodiments, atleast a portion of the coating may have an amorphous structure. As knownin the art, an amorphous structure is a non-crystalline structurecharacterized by having no long range symmetry in the atomic positions.Examples of amorphous structures include glass, or glass-likestructures. Some embodiments may provide coatings having ananocrystalline structure throughout essentially the entire coating.Some embodiments may provide coatings having an amorphous structurethroughout essentially the entire coating.

In some embodiments, the coating may comprise various portions havingdifferent microstructures. For example, the first layer may have adifferent microstructure than the second layer. The coating may include,for example, one or more portions having a nanocrystalline structure andone or more portions having an amorphous structure. In one set ofembodiments, the coating comprises nanocrystalline grains and otherportions which exhibit an amorphous structure. In some cases, thecoating, or a portion thereof (i.e., a portion of the first layer, aportion of the second layer, or a portion of both the first layer andthe second layer), may comprise a portion having crystal grains, amajority of which have a grain size greater than one micron in diameter.In some embodiments, the coating may include other structures or phases,alone or in combination with a nanocrystalline portion or an amorphousportion. Those of ordinary skill in the art would be able to selectother structures or phases suitable for use in the context of theinvention.

Advantageously, the coating (i.e., the first layer, the second layer, orboth the first layer and the second layer) may be substantially free ofelements or compounds having a high toxicity or other disadvantages. Insome instances, it may also be advantageous for the coating to besubstantially free of elements or compounds that are deposited usingspecies that have a high toxicity or other disadvantages. For example,in some cases, the coating is free of chromium (e.g., chromium oxide),which is often deposited using chromium ionic species that are toxic(e.g., Cr⁶⁺). Such coating may provide various processing, health, andenvironmental advantages over certain previous coatings.

In some embodiments, metal, non-metal, and/or metalloid materials,salts, etc. (e.g., phosphate or a redox mediator such as potassiumferricyanide, or fragment thereof) may be incorporated into the coating.

The composition of the coatings, or portions or layers thereof, may becharacterized using suitable techniques known in the art, such as Augerelectron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS),etc. For example, AES and/or XPS may be used to characterize thechemical composition of the surface of the coating.

Base material 30 may be coated to form coated articles, as describedabove. In some cases, the base material may comprise an electricallyconductive material, such as a metal, metal alloy, intermetallicmaterial, or the like. Suitable base materials include steel, copper,aluminum, brass, bronze, nickel, polymers with conductive surfacesand/or surface treatments, transparent conductive oxides, amongstothers. In some embodiments, copper base materials are preferred.

The articles can be used in a variety of applications includingelectrical applications such as electrical connectors (e.g., plug-type).The coating can impart desirable characteristics to an article, such asdurability, corrosion resistance, and improved electrical conductivity.These properties can be particularly advantageous for articles inelectrical applications such as electrical connectors, which mayexperience rubbing or abrasive stress upon connection to and/ordisconnection from an electrical circuit that can damage or otherwisereduce the conductivity of a conductive layer on the article. In someembodiments, the presence of the first layer of a coating may provide atleast some of the durability and corrosion resistance properties to thecoating. Additionally, the presence of the first layer may allow thethickness of the second layer to be reduced, thereby reducing the amountof precious metal on the article significantly.

Coating 20 may be formed using an electrodeposition process.Electrodeposition generally involves the deposition of a material (e.g.,electroplate) on a substrate by contacting the substrate with aelectrodeposition bath and flowing electrical current between twoelectrodes through the electrodeposition bath, i.e., due to a differencein electrical potential between the two electrodes. For example, methodsdescribed herein may involve providing an anode, a cathode, anelectrodeposition bath (also known as an electrodeposition fluid)associated with (e.g., in contact with) the anode and cathode, and apower supply connected to the anode and cathode. In some cases, thepower supply may be driven to generate a waveform for producing acoating, as described more fully below.

Generally, the first layer and the second layer of the coating may beapplied using separate electrodeposition baths. In some cases,individual articles may be connected such that they can be sequentiallyexposed to separate electrodeposition baths, for example in areel-to-reel process. For instance, articles may be connected to acommon conductive substrate (e.g., a strip). In some embodiments, eachof the electrodeposition baths may be associated with separate anodesand the interconnected individual articles may be commonly connected toa cathode.

The electrodeposition process(es) may be modulated by varying thepotential that is applied between the electrodes (e.g., potentialcontrol or voltage control), or by varying the current or currentdensity that is allowed to flow (e.g., current or current densitycontrol). In some embodiments, the coating may be formed (e.g.,electrodeposited) using direct current (DC) plating, pulsed currentplating, reverse pulse current plating, or combinations thereof. In someembodiments, reverse pulse plating may be preferred, for example, toform the first layer (e.g., nickel-tungsten alloy). Pulses,oscillations, and/or other variations in voltage, potential, current,and/or current density, may also be incorporated during theelectrodeposition process, as described more fully below. For example,pulses of controlled voltage may be alternated with pulses of controlledcurrent or current density. In general, during an electrodepositionprocess an electrical potential may exist on the substrate (e.g., basematerial) to be coated, and changes in applied voltage, current, orcurrent density may result in changes to the electrical potential on thesubstrate. In some cases, the electrodeposition process may include theuse waveforms comprising one or more segments, wherein each segmentinvolves a particular set of electrodeposition conditions (e.g., currentdensity, current duration, electrodeposition bath temperature, etc.), asdescribed more fully below.

Some embodiments of the invention involve electrodeposition methodswherein the grain size of electrodeposited materials (e.g., metals,alloys, and the like) may be controlled. In some embodiments, selectionof a particular coating (e.g., electroplate) composition, such as thecomposition of an alloy deposit, may provide a coating having a desiredgrain size. In some embodiments, electrodeposition methods (e.g.,electrodeposition conditions) described herein may be selected toproduce a particular composition, thereby controlling the grain size ofthe deposited material. The methods of the invention may utilize certainaspects of methods described in U.S. Patent Publication No.2006/02722949, entitled “Method for Producing Alloy Deposits andControlling the Nanostructure Thereof using Negative Current PulsingElectrodeposition, and Articles Incorporating Such Deposits” and U.S.application Ser. No. 12/120,564, entitled “Coated Articles and RelatedMethods,” filed May 14, 2008, which are incorporated herein by referencein their entirety. Aspects of other electrodeposition methods may alsobe suitable including those described in U.S. Patent Publication No.2006/0154084 and U.S. application Ser. No. 11/985,569, entitled “Methodsfor Tailoring the Surface Topography of a Nanocrystalline or AmorphousMetal or Alloy and Articles Formed by Such Methods”, filed Nov. 15,2007, which are incorporated herein by reference in their entireties.

In some embodiments, a coating, or portion thereof, may beelectrodeposited using direct current (DC) plating. For example, asubstrate (e.g., electrode) may be positioned in contact with (e.g.,immersed within) a electrodeposition bath comprising one or more speciesto be deposited on the substrate. A constant, steady electrical currentmay be passed through the electrodeposition bath to produce a coating,or portion thereof, on the substrate. As described above, a reversepulse current may also be used.

The electrodeposition processes use suitable electrodeposition baths.Such baths typically include species that may be deposited on asubstrate (e.g., electrode) upon application of a current. For example,an electrodeposition bath comprising one or more metal species (e.g.,metals, salts, other metal sources) may be used in the electrodepositionof a coating comprising a metal (e.g., an alloy). In some cases, theelectrochemical bath comprises nickel species (e.g., nickel sulfate) andtungsten species (e.g., sodium tungstate) and may be useful in theformation of, for example, nickel-tungsten alloy coatings.

Typically, the electrodeposition baths comprise an aqueous fluid carrier(e.g., water). However, it should be understood that other fluidcarriers may be used in the context of the invention, including, but notlimited to, molten salts, cryogenic solvents, alcohol baths, and thelike. Those of ordinary skill in the art would be able to selectsuitable fluid carriers for use in electrodeposition baths. In somecases, the electrodeposition bath may be selected to have a pH fromabout 7.0-9.0. In some cases, the electrodeposition bath may have a pHfrom about 7.6 to 8.4, or, in some cases, from about 7.9 to 8.1.

The electrodeposition baths may include other additives, such as wettingagents, brightening or leveling agents, and the like. Those of ordinaryskill in the art would be able to select appropriate additives for usein a particular application. In some cases, the electrodeposition bathincludes citrate ions as additives. In some cases, the citrate ioncontent may be from about 35-150 g/L, 40-80 g/L, or, in some cases,60-66 g/L.

Methods of the invention may be advantageous in that coatings (e.g.,Ni—W alloy coatings) having various compositions may be readily producedby a single electrodeposition step. For example, a coating comprising alayered composition, graded composition, etc., may be produced in asingle electrodeposition bath and in a single deposition step byselecting a waveform having the appropriate segments. The coatedarticles may exhibit enhanced corrosion resistance and surfaceproperties.

It should be understood that other techniques may be used to producecoatings as described herein, including vapor-phase processes,sputtering, physical vapor deposition, chemical vapor deposition,thermal oxidation, ion implantation, spray coating, powder-basedprocesses, slurry-based processes, etc.

In some embodiments, the invention provides coated articles that arecapable of resisting corrosion, and/or protecting an underlyingsubstrate material from corrosion, in one or more potential corrosiveenvironments. Examples of such corrosive environments include, but arenot limited to, aqueous solutions, acid solutions, alkaline or basicsolutions, or combinations thereof. For example, coated articlesdescribed herein may be resistant to corrosion upon exposure to (e.g.,contact with, immersion within, etc.) a corrosive environment, such as acorrosive liquid, vapor, or humid environment.

The corrosion resistance may be assessed using tests such as ASTM B735,entitled “Standard Test Method for Porosity in Gold Coatings on MetalSubstrates by Nitric Acid Vapor,” and ASTM B845, entitled “StandardGuide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts”following the Class IIa protocol, may also be used to assess thecorrosion resistance of coated articles. These tests outline proceduresin which coated substrate samples are exposed to a corrosive atmosphere(i.e., nitric acid vapor or a mixture of NO₂, H₂S, Cl₂, and SO₂). Themixture of flowing gas can comprise 200+/−50 ppb of NO₂, 10+/−5 ppb ofH₂S, 10+/−3 ppb of Cl₂, and 100+/−20 ppb SO₂. The temperature andrelative humidity may also be controlled. For example, the temperaturemay be 30+/−1° C., and the relative humidity may be 70+/−2%.

The exposure time of an article to a gas or gas mixture can be variable,and is generally specified by the end user of the product or coatingbeing tested. For example, the exposure time may be at least 30 minutes,at least 2 hours, at least 1 day, at least 5 days, or at least 40 days.After a prescribed amount of exposure time, the sample is examined(e.g., visually by human eye and/or instrumentally as described below)for signs of change to the surface appearance and/or electricalconductivity resulting from corrosion and/or spotting. The test resultscan be reported using a simple pass/fail approach after the exposuretime.

The coating subjected to the test conditions discussed above may beevaluated, for example, by measuring the change in the appearance of thecoating. For instance, a critical surface area fraction may bespecified, along with a specified time. If, after testing for thespecified time, the fraction of the surface area of the coating thatchanges in appearance resulting from corrosion is below the specifiedcritical value, the result is considered passing. If more than thecritical fraction of surface area has changed in appearance resultingfrom corrosion, then the result is considered failing. For example, theextent of corrosive spotting may be determined. The extent of spottingmay be quantified by determining the number density and/or area densityof spots after a specified time. For example, the number density may bedetermined counting the number of spots per unit area (e.g., spots/cm²).The spot area density can be evaluated by measuring the fraction of thesurface area occupied by the spots, where, for example, an area densityequal to unity indicates that 100% of the surface area is spotted, anarea density equal to 0.5 indicates that 50% of the surface area isspotted, and an area density equal to 0 indicates that none of thesurface area is spotted.

In some cases, the coated article that is exposed to nitric acid vaporaccording to ASTM B735 for 2 hours or mixed flowing gas according toASTM B845, protocol Class IIa, for 5 days has a spotting area density ofless than 0.10; in some cases, less than 0.05; and, in some cases, 0. Insome embodiments, the coated article exposed to these conditions has anumber density of spots of less than 3 spots/cm²; in some embodiments,less than 2 spots/cm²; and, in some embodiments, 0 spots/cm². It shouldbe understood that spotting area densities and the number density ofspots may be outside the above-noted ranges.

The low-level contact resistance of a sample may be determined beforeand/or after exposure to a corrosive environment for a set period oftime according to one of the tests described above. In some embodiments,the low-level contact resistance may be determined according tospecification EIA 364, test procedure 23. Generally, the contactresistivity of a sample may be measured by contacting the sample under aspecified load and current with a measurement probe having a definedcross-sectional area of contact with the sample. For example, thelow-level contact resistance may be measured under a load of 25 g, 50 g,150 g, 200 g, etc. Generally, the low-level contact resistance decreasesas the load increases.

A threshold low-level contact resistance value may be set wheremeasurement of a low-level contact resistance value for a sample abovethe threshold indicates that the sample failed the test. For example,the threshold low-level contact resistance value under a load of 25 gafter 2 hours exposure to nitric acid vapor according to ASTM B735 orafter 5 days exposure to mixed flowing gas according to ASTM B845,protocol Class IIa, may be greater than 1 mOhm, greater than 10 mOhm,greater than 100 mOhm, or greater than 1000 mOhm. It should beunderstood that other threshold low-level contact resistance values maybe achieved.

In some embodiments, a coated article has reduced low-level contactresistance. Reduced low-level contact resistance may be useful forarticles used in electrical applications such as electrical connectors.In some cases, an article may have a low-level contact resistance undera load of 25 g of less than about 100 mOhm; in some cases, less thanabout 10 mOhm; in some cases, less than about 5 mOhm; and, in somecases, less than about 1 mOhm. It should be understood that the articlemay have a low-level contact resistance outside this range as well. Itshould also be understood that the cross-sectional area of contact bythe measurement probe may affect the value of the measured low-levelcontact resistance.

Durability of the coated articles may also be tested. In someembodiments, durability tests may be performed in conjunction with thecorrosion tests discussed above and/or contact resistance measurements.A durability test may comprise rubbing the surface of a coated articlewith an object for a period of time and then visually inspecting thecoating for damage and/or measuring the contact resistance of thecoating. In one non-limiting example of a durability test, a counterbodymay be held against the surface of a coated article at a set load andthe coated article may be reciprocated such that the counterbody rubsagainst the surface of the coated article. For example, the counterbodymay be held against the surface of a coated article at a load of 50 g.The duration of the reciprocal motion may be measured, for example, bythe number of cycles per unit time per unit time. For instance, thereciprocal motion may be carried out for 500 seconds at a rate of 1cycle per second. In some embodiments, durability may be measured beforeand/or after subjection of an article to a corrosion test as discussedin more detail above. The contact resistance of the coating may bemeasured as described above. In some cases, the coating may be visuallyinspected for wear tracks. The wear tracks may, in some embodiments, beanalyzed by measuring the width of exposed base material between thewear tracks after a specific number of cycles under a specific load. Insome instances, the analysis may be a “pass/fail” test, where athreshold width of exposed base material between wear tracks is set suchthat the presence of a width of exposed base material above thethreshold indicates the article failed the test.

The following examples should not be considered to be limiting butillustrative of certain features of the invention.

EXAMPLES Example 1

This example compares the corrosion resistance of an article including acoating having a first layer produced in accordance with someembodiments of the invention to the corrosion resistance of two articleshaving conventional coatings. FIGS. 2A-2C each show an article afterexposure to nitric acid vapor for 30 minutes according to ASTM B0735-06.FIG. 2A shows a copper base material coated with a layer of Ni—W(approximately 40-50 microinches thick) using a pulsed reverse DCcurrent exhibiting essentially no corrosion, FIG. 2B shows a copper basematerial coated with nickel (approximately 40-50 microinches thick,electrodeposited using a Ni-sulfamate bath using a pulsed DC current)exhibiting significant corrosion, and FIG. 2C shows a copper basematerial coated with electroplated nickel-phosphorus (EP-NiP)(approximately 40-50 microinches thick, electrodeposited using a pulsedDC current) exhibiting significant corrosion. This example demonstratesthat coated articles of the invention have improved corrosion resistanceas compared to conventional coated articles.

Example 2

This example compares the durability of an article including a coatinghaving a first layer produced in accordance with some embodiments of theinvention to the durability of an article having a conventional coating.FIG. 3A shows a schematic of the test procedure for assaying thedurability of a coated article. A counterbody 100, plated with the samematerial as the wear surface, was held stationary against coated article110 with a load of 50 g while the coated article was moved reciprocallyagainst the counterbody along path 120 for 500 cycles at a frequency ofabout 1 cycle per second. FIG. 3B shows a copper base material coatedwith nickel (approximately 40-50 microinches thick, electrodepositedusing a nickel-sulfamate bath and pulsed DC current) exhibitingextensive wear tracks 130. FIG. 3C shows a copper base material coatedwith Ni—W (approximately 40-50 microinches thick, electrodeposited usinga pulsed reverse DC current) exhibiting significantly fewer wear tracks.This example demonstrates that coated articles of the invention haveimproved durability as compared to conventional coated articles.

Example 3

This example compares the corrosion resistance of articles including acoating having two layers produced in accordance with some embodimentsof the invention to the corrosion resistance of two articles havingconventional coatings. FIGS. 4A-4D each show an article after exposureto mixed flowing gas for 5 days according to ASTM B0845-97R08E01. FIG.4A-4B show a copper base material coated with a first layer of Ni—W (40microinches thick, electrodeposited using a pulsed reverse DC current)and a second layer of 20 microinch thick Au—Co alloy (FIG. 4A) or 30microinch thick Au—Co alloy (FIG. 4B) exhibiting essentially nocorrosion. FIG. 4C-4D show a copper base material coated with a firstlayer of nickel (electrodeposited using a Ni-sulfamate bath and pulsedDC current) and a second layer of 20 microinch thick Au—Co alloy (FIG.4C) or 30 microinch thick Au—Co alloy (FIG. 4D) exhibiting significantcorrosion and pitting. This example demonstrates that coated articles ofthe invention have improved corrosion resistance as compared toconventional coated articles.

Example 4

This example compares the contact resistance of articles including acoating having two layers produced in accordance with some embodimentsof the invention exposed to corrosive conditions to the contactresistance of two articles having conventional coatings exposed tocorrosive conditions. FIGS. 5A-5D quantify the low-level contactresistance of the coated articles from Example 3 and each shows theresults of multiple replicates. FIG. 5A shows the contact resistance ofa base material coated with Ni—W and 20 microinches of Au—Co alloy, andFIG. 5B shows the contact resistance of a base material coated with Ni—Wand 30 microinches of Au—Co alloy. In both cases, the contact resistancewas less than 10 mOhm, which was the threshold defined as a “pass” forthis test. FIGS. 5C and 5D show the contact resistance for basematerials coated with nickel (electrodeposited using a Ni-sulfamatebath) and 20 microinches of gold or 30 microinches of gold,respectfully. Both articles failed the contact resistance test, asindicated by the data points above 10 mOhm. This example demonstratesthat coated articles of the invention have improved contact resistanceafter exposure to corrosive conditions as compared to conventionalcoated articles.

Example 5

This example compares the contact resistance of articles including acoating having two layers produced in accordance with some embodimentsof the invention exposed to corrosive conditions to the contactresistance of two articles having conventional coatings exposed tocorrosive conditions. FIG. 6 shows stereoscope images (˜10×magnification) of a series of coated articles, each exposed to nitricacid vapor for 2 hours. The thickness of the first layer (Ni—W,electrodeposited using a pulsed reverse DC current) is listed at the topof each column and corresponds to the thickness of the first layer oneach base material in the respective column (from left to right: 20microinches, 30 microinches, and 40 microinches). The thickness of thesecond layer (Au—Co) is listed at the left of each row and correspondsto the thickness of the second coating on each base material in therespective row (from top to bottom: 4 microinches, 10 microinches, 20microinches, and 30 microinches). FIG. 7 shows a non-magnified image ofa series of coated articles, the series having the same specificationsas those in FIG. 6, where each is exposed to mixed flowing gas for 5days. FIGS. 8A-8D show contact resistance measurements for the coatedarticles shown in FIG. 7. As a control, FIGS. 9A-9B show contactresistance measurements for articles including a coating having a firstlayer of EP-NiP (electrodeposited using a pulsed DC current) and asecond layer of Au—Co after exposure to nitric acid vapor for 2 hours.This example demonstrates that coated articles of the invention haveimproved contact resistance after exposure to corrosive conditions ascompared to conventional coated articles.

What is claimed:
 1. An article, comprising: a base material; a coatingformed on the base material, the coating comprising: a first layercomprising a nickel-tungsten alloy and/or a nickel-molybdenum alloy,wherein the first layer is nanocrystalline or amorphous; and a secondlayer formed on the first layer, the second layer comprising Rh, whereinthe second layer has a thickness of less than 30 microinches, and thesecond layer is nanocrystalline or amorphous.
 2. The article of claim 1,wherein the second layer has a thickness of less than 20 microinches. 3.The article of claim 1, wherein the second layer has a thickness of lessthan 10 microinches.
 4. The article of claim 1, wherein the first layeris formed directly on the base material.
 5. The article of claim 1,wherein the second layer is formed directly on the first layer.
 6. Thearticle of claim 1, wherein the first layer and the second layer areelectrodeposited.
 7. The article of claim 1, wherein the second layercovers an entire surface of the first layer.
 8. The article of claim 1,wherein the second layer covers only part of a surface of the firstlayer.
 9. The article of claim 1, wherein the coating is free ofchromium.
 10. The article of claim 1, wherein the coating has a spottingdensity less than about 1 spot/cm² after exposure to nitric acid vaporfor 2 hours according to ASTM B0735.
 11. The article of claim 1, whereinthe coating has a spotting area density or less than about 0.10 afterexposure to nitric acid vapor for 2 hours according to ASTM B0735. 12.The article of claim 1, wherein the first layer is nanocrystalline. 13.The article of claim 1, wherein the second layer is nanocrystalline. 14.The article of claim 1, wherein the base material comprises anelectrically conductive material.
 15. The article of claim 1, whereinthe article is an electrical connector.
 16. The article of claim 15,wherein the article is a plug-type electrical connector.
 17. The articleof claim 1, wherein the weight percent of nickel is between 25-75 weightpercent.
 18. The article of claim 1, wherein the weight percent ofnickel is between 50-70 weight percent.
 19. The article of claim 1,wherein the first layer comprises a nickel-tungsten alloy.
 20. Thearticle of claim 1, wherein the first layer comprises anickel-molybdenum alloy.
 21. The article of claim 19, wherein the secondlayer has a thickness of less than 20 microinches.
 22. The article ofclaim 19, wherein the first layer is formed directly on the basematerial.
 23. The article of claim 19, wherein the second layer isformed directly on the first layer.
 24. The article of claim 19, whereinthe first layer and the second layer are electrodeposited.
 25. Thearticle of claim 19, wherein the coating has a spotting density lessthan about 1 spot/cm² after exposure to nitric acid vapor for 2 hoursaccording to ASTM B0735.
 26. The article of claim 19, wherein thecoating has a spotting area density or less than about 0.10 afterexposure to nitric acid vapor for 2 hours according to ASTM B0735. 27.The article of claim 19, wherein the first layer is nanocrystalline. 28.The article of claim 19, wherein the second layer is nanocrystalline.29. The article of claim 19, wherein the base material comprises anelectrically conductive material.
 30. The article of claim 19, whereinthe article is an electrical connector.
 31. The article of claim 30,wherein the article is a plug-type electrical connector.